The London Olympics 2012 is one of the hottest tourist tickets in the world right now.
But thousands of people who bought tickets to see synchronised swimming at London 2012 have been asked to return them - after organisers sold 10,000 too many.
When the first round of sales went live last March - when 1.9 million people entered a ballot for 700,000 tickets - synchronised swimming was an event that was not oversubscribed.
So, it was put back on sale, but a 'human data error' meant that thousands of tickets that didn't actually exist were made available.
About 3,000 customers who snapped up these 10,000 'phantom' tickets have been contacted by Games organisers Locog, and offered the chance to swap their tickets for other events for which they also applied, but were unsuccessful.
So, many of them will now get to see higher profile and more expensive events, like athletics or diving.
According to the Daily Mail, these spare tickets will be taken from the 1.3 million 'contingency' tickets that are due to go on sale this spring, which, it could be argued, will further reduce other people's chances of getting them.
A London 2012 spokeswoman told the BBC: "As a result of finalising the seating configurations in our venues and reconciling the millions of Olympic and Paralympic ticket orders against the seating plans for around 1,000 sporting sessions, we have discovered an error in seats available in four synchronised swimming sessions.
"In December we contacted around 3,000 customers who had applied for tickets in the four sessions during the second round sales process. We are exchanging their synchronised swimming tickets for tickets in other sports that they originally applied for."
Meanwhile, tomorrow is the launch of the first day when unwanted Olympic tickets can be resold at cost price.
The sale will start at 9am on the London 2012 website and run until 3 February.
It is said to be the only legal way to re-sell tickets, and has been arranged to combat the effect of ticket touts.
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